Manufacture of white lead



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2 sheets-sheet ATTORNEYS S PATENT FFH.

CHARLES I. TOLMAN, 0F NEW YORK, N. Y.,

ASSIGNOR TO NATIONAL LEAD COMPANY,

OF NEW YORK, N. Y., Av CORPORATION OF NEW JERSEY.

MANUFACTURE OF WHITE LEAD.

Application led March 15, 1921. Serial No. 452,501.

T o all whom t may concer/n.:

Be it known thatl, CHARLES P. ToLMAN, residing in New York city, New York, a citizen of the United States, have invented the following described Improvements in Manufacture of White Lead.

The invention relates specifically to the manufacture of white lead by the so-called dry process and consists in the process whereby the corrosive action of certain reagents upon metallic lead, or the material to be treatedt or corroded,'may be' facilita-ted and the quality of the productcontrolled and improved and whereby various coincident advantages are obtained in respect to cost ofV manufacture and sanitation as hereinafter made apparent. In its preferred form, the invention comprises a process for conducting the corrosivey treatment continuously and by the aid of mechanism adapted to maintain uniform reaction.

The apparatus illustrated and described in this application and also of my invention is claimed in a divisional application. filed January 26, 1922, Serial Number 531,865.

For maiiy years painters white lead has been manufactured by the so-called dryV process according to which a batch of pulverized metallic lead is tumbled in aA closed rotary cylinder in the presence of corroding reagents consisting of carbon dioxid, air, water and acetic acid. The lead is pulverized by steamblast atomization when in a molten state, and is charged into the cylinder through a door at the top when the cylinder is at rest` being at the same time sprinkled withv an aqueous solution of the acid. The cylinder is then closed and set in rotation and a flow of the gaseous reagents is passed through it in the meantime. These gaseous reagents are purified furnace gases containing C()2 and air. From time to timev the cylinder is opened by an operative who sprinkles or wets down the interior with a liquid reagent by the use of a hose, and at the end of some six or seven days the original metallic lead particles become thickly coated with, or more or less completely converted into, the vwhite basic-carbonate of lead, commercially known as white lead. Because of the presence of lumps and un'corroded lead particles, `the product of this first stage of the process, is next ground or tlireshed soas to break up the lumps and expose the metal by removing the crust from the incoiiipletely` land dryness are necessary,

l der .being allowedl corroded particles. It is then subjected to a repetition of the same corrosive treatment in another cylinder for a similar period or until substantially all of the metallic lead has been corroded, whereupon the contents of the cylinder are Washed to separate them from any still remaining metallic particles or particles of coarse carbonate. Soda is added to the Wash water to neutralize acid, and the mass is dried and packed, or ground in oil and packed as desired.

rl `he chemical reactions constituting corrosion are complex and need not to be described. They are recognized to be successive or cyclic in character onf-which ac.- countit has been assumed to be desirable to introduce the liquid reagents, by s rinkling, only at certain specified intervals on the theory that conditions of alternate wetness or at least desirable, in order to promote the desired action and produce the best results. It is the general practice to sprinkle the'corroding mass twice every twenty-four hours, both sprinklings occurring within one of the eight hour shifts of' thel day, the contents of the cylinto dry out during the following sixteen or more hours of each day. The effort to moisten thoroughly the entire dried out mass on the next succeeding sprinkling always results in such a general condition of wetness and local pastiness, as to cause the partly corroded powderous lead to ball up into lumps and also to cake and stick on the cylinder walls so that itis nec-v essary to pound the walls at frequent intervals with heavy mauls. operated by man or power to dislodge and break it up, and such pounding is a necessary part of the corrosion process as now practiced, because the agglomeration of the mass imprisons'and shields much of the metallic lead from contact wit-h the corroding reagents, and'thus not only stops or slows down the reaction but also increases the amount of lead wasted as tailings. The pounding, though necessary, is also objectionable in that it rapidly wears out the cylinders, besides which it dislodges a great deal of lead dust into the room which is poisonous to breathe, and makes it' imperative that the workers be protected.

According to the present invention, the corrosive reaction is accomplished and coiitrolled by the introduction of the liquid recarefully agent into the corroding chamber, whether of the rotary type referred to or of any other form, with the view of keeping the` until the corrosion is completed. By closely.

controlling the amount of liquid reagent, water or water and acid, introduced, and distributing it thoroughly throughout the mass and preferably so as to keep a certain percent-age constantly present therein, I have succeeded in producing the desired corrosion in a shorter period, with the use of less acid and also with marked diminution of the tendency vto ball up linto lumps or adhere to the chamber walls and without the need for the customary pounding. For this purpose the liquid does not` require to be continuously introduced but m-ay be supplied at intervals, provided the intervals are sufficienti. ly regular and provided the amount supplied 1s appropriately gauged to maintain a substantially uninterrupted semi-dry and nonpasty condition. The suitable percentage of moisture may, and should v-ary according to conditions andv requirements as later eX- plained but should not run less than two per cent nor more than live per cent, by weight referred to the moist corroding mass as the percentage base. For example, by increasing the number of sprinklings from two per day (both occurring in one of the eight hour shifts as above mentioned,) to six sprinklings per day occurring at substantially equal intervals of four hours there results an improvement in total production of upward of fifty per cent, represented by a reduction of the corrosion -period by approximately two days, the use of less reagents and the attainment of a superior product withless tailings. More frequent sprinklings under the same conditions give corresponding further improvement, and especially when the amount of liquid used. is properly coordinated -to the progress of the corrosion, that is to say, it is desirable to introduce the liquid reagent, rather freelyg during the initial stages tapering lit oif as the corrosion progressesyusing no acid during the final stages or no more than will suffice to maintain the requisite temperature for the reaction, but always adjusting the Water supply so that the necessary moisture condition will obtain as above explained.

The foregoing process `may also be performed continuously, by causing the lead to advance as a continuous or substantially continuous stream yfrom a place of feed to a place of discharge and-in the presence of the reagents which produce the corrosion. By such arrangement the. successive regions or sections of the advancing stream will correspond to successive stages in the progress of the corrosion, sequence in time being thus converted to sequence in position, which affords the advantage that each stage can be .treated with the liquid reagent according to its individual requirements and by means of automatic machinery which can be set to work with practical in fallibility vso as to maintain a uniform character of reaction at every stage and a standard output for the process both as to quantity and quality.

The accompanying drawings represent the preferred form of apparatus for continuously carrying out the process as just referred to.

Fig.' 1 represents in side elevation, a rotary corroding chamber broken away at the center and partly in section.

Fig. 2, a typical cross section of that chamber on larger scale.

Fig. 3, a longitudinal section through the feed end.

Fig. 4, anend elevation of the feed end, parts being in section,

Fig. 5 is a detail section of the automatic sprinkler shown in Fig. 2, and

Fig. 6 is a diagram of the moisture supply system.

rlhe corroding chamber consists of a long, substantially horizontal and preferably cylindrical tube l, constructed of woodenl planks or staves mortised together and vbound with circular bands 2serving as tracks by which-the chamber rests upon the rollers 3, which latter are firmly journalled on a foundation and provided with flanges is provided with annular gear racks 4 meshing with pinions 5 driven by the longitudinal power shaft 6, which rotates the chamber on the rollers. Power is applied to the driveshaft preferably at t-he middle so that the strain of driving is equally tdistributed and the drive is preferably. continuous in one direction although it might be oscillatory. The chamber shown in the drawing may be assumed to be some 95 feet long and 6 feet outside diameter, although there is no limitation'in this respect, and the annular tracks may be about six feet. apart. The chamber is interiorly lined with heavy paper 7 (Fig. 5) and covered with a layer of matched boards 8, like ordinary flooring.

thus producing a composite or laminate wall structure of excellent heatretaining qualities and hence the.least conducive to the condensation of moisture on the interior whiclrwould tend to cause the material therein to lstick to the inner surface.

The ends of the chamber are closed bv bulkheads each properly accommodated to the feed and discharge mechanisms. The bulkhead 9 at the feed end is provided with an axial aperture fitting snugly around the through which it delivers into the chamber the gaseous products of combustion received from the scrubber and which constitute the supply of carbon dioxide and air. Metallic lead pulverized in the usual Way is introduced into the chamber by the central feed spout 12, whichv is also formed in said structure between the gas spouts 11. In this position lthe gas entrances are in non-dripping relation to the feed spout so that any moisture condensing from the freshly scrubbed gas and dripping from such entrances will not Wet any part of the lead spout which would cause it to accumulate a coating and eventually an obstructing mass of lead. The pulverized or granular lead, or the material which is to be converted into White lead, is supplied to the spout,12 from an automatic feed mechanism (Fig. 4), of any suitable design but which is encased oi; enclosed within a housing. It comprises in the present case a supply hopper 13 opening onto the central part of the upper stretch of a Wide flat belt' 14, and provided with a lateral opening and an adjustable gate 15 therefor to control the rate of delivery to the belt. This gate is adjusted by the rack and pinion 16 manually operated by the worm shaft 17.

The feed belt 14 is enclosed in the upper part of a feed hopper 18 leading to the feedv spout 12 and is appropriately mounted on pulleys therein and arranged to be driven in the direction indicated so that it Will withdraw lead from the hopper gate and discharge it into the lead spout., The rate of such discharge is obviously controlled by the rotation of the belt pulleys, and such rotation is accomplished, in the-case in hand, automatically and preferably by a connection to the rotating chamber. For this purpose one of the pulley shafts is extended through the enclosing casing and driven by a sprocket and Achain 19 and a star wheel 20, the arms of which are located in position to be engaged by pins 21 projecting from the feed end bulkhead 9. By controlling the gate- 15 or the number ofr pins 21, or both. the rate of feed of metallic lead to the chamber can b'e regulated as desired and can be set to conform closely to the progress of the process.

The lead thus introduced is advanced through the chamber gravitati'onally and by the effect of the rotation of the latter. and a suitable rate of advance is secured, if the axis ot' rotation is exactly horizontal and the chamber makes say. six revolutions per "chamber". above described hour. Under the norma-l practice this Will cause 'the passage through the chamber to be made in about five days, and the lead Will in the meantime be subject. to continual agi* tation or lateral change of position as it tumbles or rolls around the interior, so that fresh surfaces of the mass are constantl presented to the action of the reagents. It7 is not necessary `to equip the interior of the chamber with lifters or vanes for promoting the travel of the lead, although these may be provided if desired. An adequate range of adjustment of the rate of advance can be secured by proper correlation of the rates of lead feed and chamber rotation.

The bulkhead 22 at the discharge end is provided with ashort extension 23 of reduced diameter, closely fitted to and revolving Within a stationary bonnet 24 which is connected to the suction side of a blower or exhaust system diagrammatically indicated at 25, the purpose of which is to cause the gaseous reagents to flow from spout 11 through the chamber and also to maintain a negative pressure, slightly less than atmosphere, Within the chamber and within the housing of the lead-feeding apparatus. The discharge end of the chamber is also equipped with a flight of curved vanes 26 for lifting the corroded lead into said reduced section 23, from which it is discharged into a suitable chamber, as for example, into the trough of the screw conveyor 27,.Which is disposed in the lower part of the enclosure 24 directly beneath the end of said reduced discharge extension 23. As a precaution against the passage jof lumps into the conveyor` which might obstruct it,the section 23 is formed with a latticed or reticulate margin as indicated at .29, the openings of which are predetermined with respect to the size of the conveyor. The lattice formation serves also to break up such lulnps as happen to be deposited upon it. by the rolling effect. A door 28, provided in the bonnet structure` affords means of access to the vchambers and closes to a position adjacent said latticed vmargin as indicated. It Will be understood, that the corroded lead'may be discharged either by continuous or intermittent delivery.'

The novel features of the rotary corroding may be usefully employed with any kind of means, for introducing the liquid reagent, .or reagents, used for corroding the lead, Whether manual or automatic. The-system herein Shown is automatic and affords special advantages in respect to the type of chamber described although it is also capable of use in the non-V continuous process, and in other relations as will presently appear. The said System involves the use of 'one or more liquid conducting pipes or passages. such as 30, permanently mounted in or on the chamber Wall and serving to conduct the liquid reagent from an outside source and distribute it, as a spray, over the mass of lead within the chamber. The pipe 30 terminates in a spray nozzle 31 which is so located when in action,

, as to direct its spray into uniformly dislead normally assumes and maintains the position indicated in Fig. 2, the rotation being in the direction of the arrow, and it is to be noted that t-he extent of inward projection of the nozzle exceeds the normal depth of the bed of lead so that its spray orifice projects above the same, and does not therefore become clogged with lead particles, when the nozzle pipe is carried through the lower part of its path and the vlead tumbles over or around it. The spray nozzle and also such other parts ofthe moisture supply system as are exposed to the interior of the chamber, are sofarranged, or otherwise so constituted, as to vprevent rapid escape of heat through them to the exterior (the corrosion reaction being exothermic) so that their surface temperature is thus caused to approximate that of the gases in the chamber, or at least, is kept above their dew point. This may be accomplished by making said parts of a material of poor heat Vconducting quality, or by appropriately heat-insulating them when they are made of metal, and the latter method is employed herein. Such "'heat protection insures against the condensation of moisture on s'aid parts and thereby prevents the accumulation of heavy masses of corroded lead upon them. In the present case theI nozzle pipes 30 are double-Walled or jacketed with a surrounding pipe 32 forming an intervening air space which is sufiicient to make them non-condensing. The space between the pipes also accommodates a hammer 33, in the form of an annulus embracing the inner pipe and adapted to slide thereon. When the nozzle pipe attains a sufficiently dependent position this hammer slides down it, and by lts impact against the nozzle head jars loose any lead which may have adhered to it, thus keeping it clean. A rounded or bevel-ended collar 34 on the pipe 30 serves to detain the hammer in its outermost position as the pipe approaches vertically so 'that the hammer does not slip off the collar until the pipe is nearly vertical, thus insuring the delivery of a vigorous blow. The subsequent inversion of the pipe, consequent on the continued rotation of the chamber, restores the hammer to its outermost position.

To such non-condensing pipe and nozzle mechanism, the liquid reagent may be sup- `plied in any appropriate way adapted to cause the delivery therethrough of a suitable amount of liquid at a suitable spraying pressure. In the case in hand the pipe member 30 is directly connected to, and forms the discharge outlet of, a receptacle 35 mountedon the outside of the chamber wall in a position to be carried thereby into a tank of liquid 36 located directly beneath the chamber. The receptacle is provided with a filling hole 37 by which it is charged with the liquid during immersion, as it passes through thev tank, rand with an adjustable overflow tube 38 which prescribes the amount of liquid remaining in the receptacle as it leaves the tank. The outlet from this clipper-receptacle is controlled by a disc valve 39 operated by-a weighted lever 39a, so that the outlet remains closed during the process of filling and is not opened until the rotation of the corroding chamber has carried the center of gravity of the lever over its fulcrum support. This does not occur until the nozzle 31 assumes substantially the angle indicated in Fig. 2 in which it is in the correct position above referred to and wherein the elevation of the dipper above the nozzle provides a sufficient hydrostatic head to produce vigorous spraying and spread the liquid out in a fan-shaped spray over a considerable area of the lead mass, but not upon the chamber wall. The liquid reservoirs 36 are connected by piping 40 with a main water supply tank 43 (F ig. 6), wherein the level is controlled, as by means of a float-valve 44 or otherwise at the level desired for the several reservoirs. They are also connected by piping 41-with a similar float-controlled supply tank 45 containing an acid reagent and appropriate valve connections 42 are provided so that the liquid in each reservoir may contain either water or acid solution. or be cut out of action, as desired. The tank 45 of acid reagent will be understood to be supplied from another source 46 in which appropriate proportions of water andacid are measured and mixed together.

Vhen the above described system is employed for the continuous process of this invention the spray nozzles are distributed at successive points along the chamber'so that they will operate on successive zones of the advancing lead stream and inasmuch as thev deliver but a small amount of liquid on each rotation and deposit it on the constantly changing surface of the lead mass, the effect vis to produce a homogeneous admixture of the liquid with the lead, which is well adapted to maintain the semi-dry condition and keep the moisture percentage under control or within the limits already referred to.

y The process is generally carried out in efficient chemical contact with the reagent,

and this will be found to occur in about five days in the operations as described. The conveyor 27 conducts the lead discharged from the first chamber to the threshing or pulverizing app'arat'is'wherein the metallic particles are freed from their coatings and made'accessible for further'contact with the corroding reagents. vFrom this operation the partially corroded mass is conveyed and fed into a second corroding chamber which may be exactly like the first, and the transit through this second chamber results in the corrosion of substantially all of the remaining metallic lead, the resulting product being then ready for washing, in order to neutraliz'e the remaining acid, and the other usual finishing steps. For the chamber working on the first stage the several dippers and their liquid supply'means are set so that in the first three or four spray zones the lead is liberally supplied with acid solution; the remaining nozzles are set to spray with Water only, or with a weaker acid solution according to the amount supplied in the earlier zones except as to the last two or three zones, which may be cut off entirely or used for either water or acid as the moisture conditions require. In this way the rate of supply of acid to the mass is diminished as the corrosion progresses. For the -second corrosion also, the acid is similarly regulated, the first zone only reveiving acid solution and the rest only water, excepting those which are cut out as the moisture conditions happen to require, and it is generally desirable to allow the mass to dry out as it approaches the termination of the rst corrosion. In

both stages, the amount of acid required to sandy The exact causesof the development of coarser particles have not heretofore been understood, but I have ascertained that their production depends upon, and can be controlled by, the moisture condition during corrosion. That is to say, if the process be run relatively dry the effect is to make larger particles and if run moister, to make finer particles and I set the adjustment of the spray system accordingly, bearing in mind that the moisture condition is generally somewhat higher in the immediate proximity of the spray points than between them, and I allow for this variation or make use of it, for the purpose stated, that is to say, by adjusting the system so that the advancing stream will, for a suitable time in the aggregate, contain that greater percentage of moisture which yields the finest size particles and for the rest of the time will contain less moisture suited to yield the coarser particles. It is not a difficult matter to ascertain the relative proportion or degree of coarseness in the corroded product and with this information in hand it is easily possible to vary the numb'er of spray nozzles in action or the amount of their deliveries, so that the aggregate time of relatively moist corrosion shall bear the proper relation to the aggregate time of the less moist corrosion and thereby produce the exact quality of white lead that may be required for a given purpose. My invention thus consists in the control of the duration of the relatively more moist and the relatively less moist corrosion periods to the end of controlling the proportional amount of the coarser particles and also the size thereof,

and by such means I 4am enabled to obtain the desired finished product with the least loss in the form of tailings. Sampling 'holes are provided at frequent intervals along the chamber, though not shown in the drawings, and by means of these the moisture condition within may be ascertained from time to time, but it will be apparent that once the moisture system has been properly set it is not likely to require change except as the result of a change in the 'rate of flow vor the relative humidity of the gas flow. With gas taken direct from the scrubbers the relative humidity is substantially constant and with appropriate regulation the flow variation may also be kept within reasonable limits.

I claim' the followings.

1. In the process of making white lead by the corrosive action of carbon dioxide, air, water and an acid, upon an agltated mass of ranular metallic lead, the' improvement which consists in admitting the .Water in amount predetermined and adapted to keep the mass in a moist but non-pasty condition, without substantial'interruption during the course of treatment.

2. In the process of making white lead by I the corrosive action of carbon` dioxide, air,

Water and acetic acid upon an agitated mass of granular metallic lead, the improvement which consists in admitting the Water in small amounts at predetermined substantially regular intervals so as to keep the course of treatment.

lead mass from becoming or remaining dried out for any substantial perlod during the of va gaseous reagent and spraying a liquid reagent thereover so as to maintain the granular mass in a moist but non-pasty condition. l

5. The process of corroding lead which consistsv in tumbling pulverized lead in a rotary chamber in the presence of a gaseous reagent and spraying liquid reagent therein only to such extent and in such manner as Will suice for producing lthe corrosive reaction Without producing caking on the rotating chamber wall.

6. The process of corroding lead which consists -in agitating pulverized lead in the presence of gaseous and liquid reagents While maintaining not less than 2% or more than 5% of moisture lin the mass.

7. The process of corroding lead which consists in agitating pulverized metallic lead in a chamber in contact with a gaseous reagent, adding' an aqueous reagent containing acid to the mass at a rate adapted to keep the massfrom becoming dried out, and diminishing the amount of acid supplied as the corrosion progresses.

8. The process of corroding lead which consists in tumbling pulverized lead in a rotary chamber, causing a gaseous reagent containing air and carbon dioxide to flow in contact with the tumbling lead, and spraying the lead with an aqueous reagent containing acetic acid, atsubstantially regular intervals adapted to keepthe mass from becoming dried out and also from caking on the Walls of said chamber.

9. The process of corroding lead which consists in tumbling the lead in a rotary chamber, admitting a gaseous reagent thereto, spraying the lead with an aqueous reagent during the chamber rotatlon and diminishing the admisslon of aqueous reagent as the corrosion progresses.

10. The process of corroding lead which consists in passing granular metallic lead together with a flow' of gaseous reagent,

through a corroding chamber and supplying moisture thereto in amount adapted to keep the lead in a moist but non-pasty condition.

11. The process of makingv White lead which comprises advancing metallic'lead as a continuous agitatedV stream through a corroding chamber in the presence of a gaseous reagent and introducing a liquid reagent into said chamber at such rate and in such distribution along the stream as to maintain a general moisture condition therein of not less than 2% nor more than 5%.

12. The process of making White lead which comprises introducing pulverized lead into one end of a corroding chamber, agitating *and advancing the same through the chamber in the presence of carbon dioxide, introducing'an aqueous reagent containing acetic acid near the feed end of said chamber and an aqueous reagent With less or no acid near the discharge end thereof.

13: The process of corroding lead Which conslsts in advancing granular metallic lead .through a corroding chamber maintaining the advancing stream in constant agitation so. as to expose fresh surfaces for contact with a gaseous reagent in said chamber, and spraying the agitated lead stream with an aqueous reagent atpoints distributed along its course through the chamber. i

14. The process of making Whlite lead which comprises introducing pulverized metallic lead into one end of a rotary corroding chamber, advancing the same therethrough by tumbling it therein maintaining a gaseous reagent Within the chamber, spraying the mass With an aqueous reagent and delivering corroded lead from th'e other end of the chamber.

15. The process of making White lead Which comprises advancing metallic granular lead, through a rotary corroding chamber by tumbling it therein` passing a gaseous reagent through the chamber, and introducing a liquid reagent into said chamber. in amount suited to maintain the mass in a semi-dry condition containing not less than 2% of moisture.

1G. The process of making White lead which comprises feeding pulverized lead into one end of a horizontal rotaryv chamber allowing it to advance through the chamber solely by the effect of tumbling in said horizontal chamber, supplying corrosive reagentsI to the chambery and delivering corroded lead from the. other end of the chamber.

17. The process of making White lead which consists in advancing a continuous stream of pul-verized lead through a corroding chamber' in the presence of a gaseous reagent and distributing a liquid reagent thereto at successive points along the stream, pulverizing or threshing the partially corroded lead discharged from said chamber. admitting it to a second corroding chamber and advancing the same therethrough in the presence of a gaseous reagent and distributing a liquid reagent to said second chamber at successive points along the length thereof.

18. The process of making white lead which consists in advancing by tumbling a continuous stream of pulverized metallic lead through a horizontal rotary corroding chamber, passing a gaseous reagent `into the chamber and distributing a liquid reagent thereto at successive points along the stream, threshing the partially corroded lead discharged from said chamber, feeding the same to a second corroding chamber and advancing by tumbling the same therethrough as a continuous stream, in the presence of a gaseous reagent, and distributing a liquid reagent to said advancing stream at successive points along the length thereof.

19. In the process of making White lead by tumbling pulverized metallic lead While supplying corrosive gaseous and liquid reagents thereto, the improvement which consists in maintaining a different moisture percentage in the mass at different periods of the corrosive action, and producing a quantum of coarse` particles in the corroded product by increasing the period of corrosion at the lower percentages of moisture.

20. The process of making White lead which consists in agitat-ing and advancing a stream of lead particles, maintaining dii ferent percentages of moisture in dierent parts or zones of the stream and varying the length of the relatively dry Zones for the purpose and with the result of producing variable degrees of coarseness in the corroded product.

In testimony whereof. I have signed this specification.

ICHARLES P. TOLMAN. 

